Speaking-telephone



(No Model.) F. BLAKE SPEAKING TELEPHONE. No. 250,128. Patented Nov.29,1881.

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UNITED STATES PATENT OFFICE.

FRANCIS BLAKE, OF WVESTON, MASSACHUSETTS.

SPEAKING-TELEPHONE.

SPECIFICATION forming part of Letters Patent No. 250,128, dated November29, 1881.

Application filed September 15, 1881. (No model.) Patented in EnglandJanuary 20, 1879, in Canada May :28, 1870, in Italy May 20,

1880, in New South Wales July 20, 1880, in Cape of Good Hope August 30,1880, in Natal September 6, 1880, in Spain November 5, 1880, in PortugalNovember 10, 1880, and in British Guiana March 523, 188].

To all whom it may concern Be it known that I, FRANCIS BLAKE, ofWVeston, in the State of Massachusetts, have invented certain new anduseful Improvements in Speaking-Telephones, ofwhich the following is aspecification.

My said improvements relate to that form of transmitting-telephone inwhich the undulations or variations in the strength of an electriccurrent necessary for reproducing sounds in areceivin g-instrument areproduced by varyin g the resistance of the circuit through chan ges ofpressure between two electrodes of the circuit.

As heretofore constructed, one of the electrodes in such instruments isheld in fixed position, while the other, being free to move to someextent, is constantly held in contact with such fixed electrode, and ispressed against it with greater or less force by the vibrations of thediaphragm with which itis connected. In using an instrument of this formit has been found necessary to adjust the initial static pressurebetween its electrodes with great care and delicacy, in order to securesuch a variation of resistance between them under the vibrations of thediaphragm as will enable the current to reproduce in areceiving-instrument the sounds which fall upon thetransmittinginstrument. WVhen such an adjustment has been secured it iseasily disturbed by slight causes, such as a change in the temperatureof the instrument or a trifling movement of some of its parts inrelation to other parts.

By my inventions, some of which form the subject-matter of applicationsalready pending or to be filed for separate patents, the proper adjustment is easily secured, and is not liable to be disturbed in thepractical use of the instruments. The present application has referenceto a device employed for insuring the contact of the electrodes underall circumstances. I support both electrodes in such a manner that theycan move freely with the diaphragm. The outer electrode, or the one awayfrom the diaphragm, is supported so as to move freely, but is made soheavy, or is so weighted, that by its inertia it will ofi'er aresistance to the slight and quick vibrations of the diaphragm, whichwill give a varying pressure between the electrodes and a consequentchange in the resistance of the circuit; and itis so supported that theinitial static pressure between the two electrodes will not be sensiblyaifected by a change of temperature within the ordinary range oftemperatures to which such instruments are exposed. It is on the end ofa spring, the other end of which is connected to a lever by means ofwhich the proper initial pressure between the electrodes and against thediaphragm is obtained. To secure contact between the electrodesindependently of the pressure against the dia phragm I support the onenext to the diaphragm upon a spring which exerts its pressure againstthe opposite electrode.

The manner in which I construct instruments embracing my invention isshown in the drawings hereto annexed, in which- A represents a box orcasing, in which the mechanism of a telephone embracing my improvementsis inclosed. This mechanism is, for convenience, attached to the coveror top of the box A.

Figure 1 is a plan of the mechanism attached to the top or cover of thebox. Fig. 2is asection of the box and mechanism, taken through themiddle, on the dotted line m w of Fig. 1, and showing one of thescrew-cups for making connections with the exterior circuits. Fig. 3 isa cross-section of the box and mechanism on the dotted line :0 ac ofFigs. 1 and 2, and showing the screw-cups for making connections withthe exterior circuits.

B represents a metal ring or frame for holding the mechanism of thetelephone. It is screwed to the cover A, as shown, and has two ears, B BOn the inner surface of the ring B is a narrow ledge or lip, 11, onwhich the diskordiaphragmGisplaced. Thisdiaphragm is formed, as usual,of a thin iron plate. A lining of paper or other suitable material isplaced between it and the ledge or lip, and it is held in place by twosprings, D D, attached to the metal rim or ring B, with their freeendspressing upon the back of the diaphragm, near its center, so as to holdit against the ledge.

Thin pads of rubber to a, are placed between the ends of the springs andthe diaphragm. By this method of holding the diaphragm in place it islessliabletobedistorted byachange of temperature than when held whollyat its circumference.

The center of the ring and diaphragm is placed opposite the orifice E inthe cover A, through which the sounds enter the instrument. On the otherside of the diaphragm, and at its center, is placed the inner electrode.It is a small metal bar, 0, one end of which rests against thediaphragm, while the other end is brought nearly to a point, and is incontact with the outer electrode, 6, and is best formed or" or platedwith some metal, like platinum or nickel, which is not easily corroded.ltissupported independently, as shown and as previously stated, ,upon alight spring, 0, which tends to press it away from the diaphragm and toward the opposite electrode. This method of supporting the electrodeinsures its contact with the other electrode under some circumstances,when otherwise they would be liable to be separated and the circuitbroken. The other electrode, 0, is formed on a weighted spring, (7,which is supported on an adjustinglever, F, by which the tension of thespringis regulated. This spring must be stronger than the spring 0,which supports the electrode 6, and from its greater strength it tendsto keep the electrode 6 in contact with the diaphragm. Itismadeof apieceof acommon watch-spring, and it carries at its free end a weight, g,heavy enough to check very greatly the rate of vibration of the spring.This weight may be of metal, which may serve directly as the electrode;but I have obtained better results by applying to it, at thepoint ofcontact with the other electrode, a piece of gas-coke or a hardpressedblock of carbon, such as is used for electric lights. The employment ofthe coke or carbon does not, however, constituteapart of any of myinventions, further than it contributes a portion of the weight carriedby the spring. If the weight is a non-conductor, as it may be, theremust be a metallic conductor between the carbon or otherelectrode usedand the spring or some other part of the circuit.

The weight must be proportioned to the stiffness of the spring, a stiffspring requiring a heavier weight than a weaker one.

The adjusting-lever F, to an arm of which one end of the spring d isattached, is a stiff bar connected at one end by a stiff spring, j, tothe ear B of the ring B. The other end rests upon an adj usting-screw,G, placed in the ear ]3 on the opposite side of the ring. The spring jtends to force. the lever F away from the diaphragm and against theadjusting-screw G. The ear B supporting the adjusting-screw G, isdrilled and slotted, as shown in Figs. 1 and 2, to prevent the screwfrom wearing loose. The part of the lever F which comes incoutact withthe screw is inclined to theaxis of the screw, as shown, so that whenthe screw is forced inward it will press the lever toward the diaphragm,and when it is withdrawn the lever will, by the tension of the spring j,be forced away from the diaphragm. The outer end of the screw extendsinto a hole, I, through the casing, and is fitted to receive a key, bywhich it can be turned to adjust the lever to a desired position.

The pressure between the two electrodes and against the diaphragmobviously depends upon the position given to the adjusting-lever by theadjusting-screw G; but it is obvious that, as this pressure can beincreased or diminished only by increasing or diminishing the tension ofthe spring d, the changes in the pressure by turning the screw will bemuch less rapid than they would be if the electrode were acted upondirectly by the lever or the adjusting-screw. Hence a proper adjustmentof the initial static pressure between the electrodes can be much moreeasily obtained through the agency of the spring d than without it. Itwill also be easily seen that this pressure will not be sensiblyaffected by any slight change in the position of the electrodes whichmight arise from the expansion or contraction of any part of theapparatus under a change of temperature. On the other hand, it will beseen that if the diaphragm is thrown into the rapid but slightvibrations caused by sounds, the spring alone would yield to them soreadily as to give but little change of pressure between the electrodeswithin the range of the vibrations; but by reason of the inertia of theweight the tendency of the spring to follow the vibrations of thediaphragm will be checked, and a greater range of pressures between theelectrodes will be obtained. At the same time it is easy to see that thechanges of pressure will be very difl'erent from what they would be ifthe electrode were supported rigidly and could not'yield to themovements of the diaphragm.

For convenience in construction, I attach the spring 0 to the same armof the adjusting-lever F to which the spring (1 is attached, andseparate the two springs c and d by'a piece of insulating substance, 1';but the spring 0 might be attached to any convenient portion of theinstrument, if properly insulated.

The wires for connectiug the transmittinginstrument with thereceiving-telephone are marked w and w. I have, however, shown them asconnected with the primary circuit of an induction-coil, I, inconnection with which 8 and s are the screw-cups leading to the battery, while 8 s are screw-cups for connecting the line-wires with thesecondary circuit of the coil I.

The use of the induction-coil is not essential, and the wires w w may goat once to the re ceivinginstrument. The wire w is connected directlywith the spring-arm 0 of the electrode 6, as shown in Fig. 2. The wire wis connected with one of the ears of-the ring 13, as shown in Fig. 3,which is in metallic connection with the electrode 6, as shown in Fig.2.

In applications already pending for patents for improvements inspeaking-telephones, the first of which was filed January 3, 1879, Ihave described and shown precisely the same instrument herein describedand shown. The object of the present application is to secure, by adivision of the said application of J anuary 3,1879, a separate patentfor the improvement in said instrument, which is hereinabove especiallyreferred to as gained by supporting the inner electrode, 6, upon theindependent spring 0, acting in a contrary direction to the strongerspring d, which carries the outer electrode and maintains the requiredinitial pressure between the electrodes and against the diaphragm. Allother inventions made by me and embodied in the said instrument areherein dis- FRANCIS BLAKE.

Witnesses:

JOHN H. ROBERTS, A. S. TWITOHELL.

